JP2005063731A - Nonaqueous electrolyte secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery enhancing safety and charge/discharge cycle performance by forming a stable lithium ion conductive film on the surface of metallic lithium or a lithium alloy. <P>SOLUTION: The nonaqueous electrolyte secondary battery has a positive electrode 1, a negative electrode 2 containing lithium or the lithium alloy, and a nonaqueous electrolyte, and a film 6 containing silicon oxide, silicon sulfide, lithium oxide, and lithium sulfide is formed on the surface of the negative active material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

In recent years, as various electronic devices have advanced functions, expectations for higher performance of secondary batteries used as their power sources are increasing. Lithium ion batteries using lithium cobaltate (LiCoO ₂ ) or lithium nickelate (LiNiO ₂ ) for the positive electrode and graphite or hard carbon for the negative electrode are more energy efficient than conventional lead storage, Ni-Cd batteries and nickel-hydrogen batteries. High density. However, the mounting energy density of lithium ion batteries is approaching its limit, and it has become impossible to satisfy the needs of various electronic devices.

  Thus, the use of lithium alloys such as metallic lithium and lithium-silicon alloys as the negative electrode active material has been reviewed. Metallic lithium and lithium alloys have a low potential and show a large theoretical capacity. Combining these negative electrode active materials with metal oxides or sulfur-based positive electrode active materials yields non-aqueous electrolyte secondary batteries that exhibit high energy density. Therefore, as negative electrode active materials for next-generation high energy density secondary batteries. Promising.

  However, metallic lithium is highly active and reacts with the electrolyte to form a solid electrolyte interface (SEI) layer. The SEI layer grows during long-term storage of the battery or with charge / discharge. Furthermore, dendritic or powdery lithium is also easily formed with charge and discharge. This not only causes safety problems and loss of active material of the lithium battery, but also causes internal short circuit of the battery.

  Therefore, the use of solid electrolytes has been proposed to improve the charge / discharge efficiency and safety of metal lithium batteries. Among them, the application of a glass solid electrolyte has attracted attention. Known glass solid electrolytes include lithium halide, lithium nitride, lithium oxyacid salt, and derivatives thereof.

Further, Li ₂ S—SiS ₂ , Li ₂ S—P ₂ S ₅ , Li ₂ S—B ₂ S _{3 and} other lithium ion conductive sulfides (glass solid electrolytes), and these glass solid electrolytes such as LiI A method of doping lithium halide, Li ₃ PO ₄ , Li ₄ SiO ₄ or the like has been studied.

In particular, a lithium ion conductive glass solid electrolyte doped with Li ₄ SiO ₄ is reported to show a high lithium ion conductivity of 10 ⁻⁴ to 10 ⁻³ S / cm near normal temperature. 2.

  These glass solid electrolytes are produced by a rapid cooling method using twin rolls or a mechanical milling method. In addition, for the purpose of protecting metallic lithium, a technique in which a glass solid electrolyte is directly formed on a lithium metal surface by a sputtering method is also disclosed in Non-Patent Document 3 and Patent Document 1, and these glass electrolytes or glass electrolytes are also disclosed. Research and development of the all-solid-state secondary battery used is underway.

  Further, metals and metalloids such as Si, Ge, Al, and Sn are easily alloyed with lithium, can absorb a large amount of lithium, and have a high capacity. However, it is known that these metals or metalloids undergo an alloying / dealloying reaction with lithium during charging and discharging, and show a large volume change at that time. Due to this large volume change, there is a problem that the alloy phase is pulverized, current collection is poor, and a side reaction with the electrolytic solution occurs, resulting in a significant reduction in discharge capacity.

  In order to solve these technical problems, it has been proposed to use a method using fine particles and a thin porous membrane. However, an alloy material having a high mounting capacity and good cycle performance has not yet been obtained.

On the other hand, since sulfur has a high specific capacity (1675 mAh · g ⁻¹ ), its use as a positive electrode active material for non-aqueous electrolyte secondary batteries has been studied for a long time. For example, research on a lithium / sulfur secondary battery operating at room temperature using sulfur for the positive electrode and lithium for the negative electrode was reported in Non-Patent Document 4 and Non-Patent Document 5 20 years ago.

In these reports, soluble lithium polysulfide (Li ₂ S _12.2 ) is used as the positive electrode active material, and the current density for charge / discharge characteristics, the type of solvent used in the non-aqueous electrolyte, temperature, active material concentration, etc. However, the problem of short charge / discharge cycle life and low utilization rate of sulfur could not be solved, so that a battery at a practical level could not be obtained.

  Yaman et al. Reported the results of detailed studies on lithium / sulfur secondary batteries in Non-Patent Document 6 and Non-Patent Document 7.

  Furthermore, Cho et al. Improved the utilization rate of sulfur, which is a positive electrode active material, and sulfided between the positive and negative electrodes by attaching a protective coating made of a glass solid electrolyte to the surface of the lithium negative electrode or optimizing the electrolyte. Patent Documents 2, 3 and 4 disclose attempts to block the generation of shuttle current by repeated chemical redox of the product.

JP 2000-340257 A

US Pat. No. 5,523,179 US Pat. No. 5,814,420 US Patent No. 6,025,094 S. Kondo, K .; Takada, Y .; Yamamura, Solid State Ionics, 53-56 (1992) 1183 K. Hirai, M .; Tatsumisago, T .; Minami, Solid State Ionics, 78 (1995) 269 S. J. et al. Visco, U. S. Pat. 6,025,094 (2000) R. D. Rauh etc. , 21st IECEC, P283 (1977) R. D. Rauh etc. , J .; Electrochem. Soc. , 126, 523 (1979) Yamin etc. , J .; Electrochem. Soc. , 135, 1045 (1988) Yamin etc. , J .; Power Sources, 9, 281 (1983)

In a non-aqueous electrolyte secondary battery using metallic lithium or a lithium alloy as a negative electrode, cycle performance and battery safety are improved by forming a sulfur-based glass solid electrolyte on the negative electrode surface. However, this sulfur-based glass electrolyte is decomposed even in an environment having a water content of 20 ppm or less, and there is a risk that toxic H ₂ S gas is generated, and the function as an electrolyte is lost. Moreover, when force is applied, the sulfur-based glass solid electrolyte may crack and be destroyed. In addition, when a sulfur-based glass solid electrolyte is used, a film-like sulfur-based glass solid electrolyte is prepared in advance or directly formed on the surface of metallic lithium or a lithium alloy, resulting in an increase in mass production cost. was there. As described above, the sulfur-based glass solid electrolyte has significant problems in terms of handling method, storage method, mechanical strength, and mass productivity.

  Therefore, the present invention solves such problems and forms a stable lithium ion conductive coating on the surface of metallic lithium or lithium alloy, thereby providing a non-aqueous electrolyte that has excellent safety and charge / discharge cycle performance. The object is to provide a secondary battery.

  The present inventor conducted extensive research on the coating film on the surface of metallic lithium or lithium alloy, and found the following findings.

  The invention of claim 1 is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing lithium or a lithium alloy, and a non-aqueous electrolyte. On the surface of the negative electrode active material, silicon oxide, silicon sulfide, lithium oxide and sulfide A film containing lithium is formed.

  According to the invention of claim 1, the negative electrode active material surface is coated with a lithium ion conductive film having Si—O and Si—S as a skeleton, and side reactions due to contact between the negative electrode active material and the electrolytic solution are suppressed, A nonaqueous electrolyte secondary battery having excellent charge / discharge cycle performance can be obtained.

  A second aspect of the present invention relates to a method for producing a nonaqueous electrolyte secondary battery according to the first aspect of the present invention, wherein a negative electrode active material comprising lithium or a lithium alloy having amorphous silicon oxide formed on the surface thereof is used as a polysulfide anion. It is characterized by passing through a step of contacting with a non-aqueous solution containing.

  According to invention of Claim 2, the surface of a lithium containing negative electrode active material is coat | covered with the new protective layer of the amorphous silicon oxide strong against moisture, and the negative electrode plate which does not generate | occur | produce poison gas is obtained. In the present invention, “amorphous silicon oxide” refers to a compound represented by the general formula SiOx (O <x <2). Also, just before the battery is assembled, this protective layer reacts with polysulfide anions to form a lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide. It is possible to produce a non-aqueous electrolyte secondary battery excellent in the above.

  A third aspect of the present invention relates to a method for producing a nonaqueous electrolyte secondary battery according to the first aspect, wherein a negative electrode in which amorphous silicon oxide is formed on the surface of a negative electrode active material made of lithium or a lithium alloy is used. After assembling the battery, a non-aqueous electrolyte containing a polysulfide anion is injected.

  According to the invention of claim 3, by injecting a non-aqueous electrolyte containing a polysulfide anion, lithium ions containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide are formed on the surface of the lithium-containing negative electrode active material. Since the conductive coating is formed on the spot, the process is simple, the influence of moisture is avoided, the production process is advantageous, and a non-aqueous electrolyte secondary battery excellent in charge / discharge cycle performance can be manufactured.

  The invention of claim 4 relates to a method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein a negative electrode in which amorphous silicon oxide is formed on the surface of a negative electrode active material made of lithium or a lithium alloy, and sulfur After assembling a battery using a positive electrode containing, a non-aqueous electrolyte is injected to charge / discharge the battery.

  According to the invention of claim 4, a polysulfide anion soluble in the electrolyte is generated from sulfur in the positive electrode, which moves to the negative electrode, and includes silicon oxide, silicon sulfide, lithium oxide and lithium sulfide on the negative electrode surface. A nonaqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics using a negative electrode in which a lithium ion conductive film is formed and the negative electrode surface is protected with a lithium ion conductive film can be produced.

  Invention of Claim 5 is related with the manufacturing method of the nonaqueous electrolyte secondary battery of Claim 1, and the negative electrode which formed the amorphous silicon oxide on the surface of the metal or metalloid which forms an alloy with lithium, A battery is assembled using a positive electrode containing a lithium composite oxide in a discharged state, and then a non-aqueous electrolyte containing a polysulfide anion is injected to charge / discharge the battery.

  According to invention of Claim 5, the polysulfide anion in electrolyte solution moves to a negative electrode, and lithium ion conductivity containing silicon oxide, silicon sulfide, lithium oxide, and lithium sulfide is formed on the negative electrode surface by charge / discharge of the battery. A nonaqueous electrolyte secondary battery in which a coating is more reliably formed and has excellent charge / discharge cycle characteristics can be produced.

  Invention of Claim 6 is related with the manufacturing method of the nonaqueous electrolyte secondary battery of Claim 1, and the negative electrode which formed the amorphous silicon oxide on the surface of the metal or metalloid which forms an alloy with lithium, After assembling a battery using sulfur and a positive electrode containing a lithium composite oxide in a discharged state, the battery is charged and discharged by pouring a non-aqueous electrolyte.

  According to the invention of claim 6, a polysulfide anion soluble in the electrolytic solution is generated from sulfur in the positive electrode, and this anion moves to the negative electrode. By charging / discharging of the battery, silicon oxide, silicon sulfide, and oxidation are formed on the negative electrode surface. A lithium ion conductive coating containing lithium and lithium sulfide can be more reliably formed, and a nonaqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics can be produced.

  In the non-aqueous electrolyte secondary battery of the present invention comprising a positive electrode, a negative electrode containing lithium or a lithium alloy, and a non-aqueous electrolyte, silicon oxide, silicon sulfide, lithium oxide and lithium sulfide are provided on the surface of the negative electrode active material. Since the lithium ion conductive coating is formed and the coating on the negative electrode surface suppresses side reactions between the negative electrode active material and the electrolytic solution, a nonaqueous electrolyte secondary battery exhibiting excellent cycle life can be obtained.

  As a method for forming a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide on the surface of the negative electrode active material, amorphous silicon oxide is previously formed on the surface of the negative electrode active material containing lithium or a lithium alloy. The anode active material is contacted with a non-aqueous solution containing a polysulfide anion, a battery is assembled, a non-aqueous electrolyte solution containing a polysulfide anion is injected, and the positive electrode contains sulfur. In addition, a method of charging / discharging after injecting a non-aqueous electrolyte, a negative electrode in which amorphous silicon oxide is formed on the surface of a metal or metalloid that forms an alloy with lithium in advance, After assembling a battery using a positive electrode containing a lithium composite oxide, a method of charging and discharging the battery after injecting a non-aqueous electrolyte containing a polysulfide anion, and containing sulfur in the positive electrode In addition, by injecting a non-aqueous electrolyte and then taking a production method such as a method of charging / discharging the battery, the surface of the negative electrode active material can be more easily and more reliably coated with silicon oxide, silicon sulfide, lithium oxide and A lithium ion conductive coating containing lithium sulfide can be formed.

  The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode containing lithium or a lithium alloy, and a non-aqueous electrolyte, and lithium containing silicon oxide, silicon sulfide, lithium oxide, and lithium sulfide on the negative electrode active material surface. An ion conductive film is formed.

  The present invention also relates to a method for producing the above non-aqueous electrolyte secondary battery, wherein a negative electrode active material made of lithium or a lithium alloy having amorphous silicon oxide formed on the surface thereof, a non-aqueous solution containing a polysulfide anion and It is characterized by undergoing a contact process. The non-aqueous solution preferably contains an ether-based or ester-based organic solvent.

In the present invention, first, amorphous silicon oxide is formed on the surface of the negative electrode active material made of lithium or a lithium alloy by spray spray plating, sputtering, or vacuum deposition plating. Amorphous silicon oxide is represented by the general formula SiO _x (where 0 <x <2).

  Next, when the negative electrode active material having amorphous silicon oxide formed on the surface is brought into contact with a non-aqueous solution containing a polysulfide anion, local cell reactions of formulas 1) to 4) occur.

SiO + Li (M) → a-SiO _x + Li _b Si + Li ₂ O (1)
^{_{Li b Si + S y n- →}} a-SiS 2 + Li b S z-2 (2)
_{Li x S z-2 + Li} (M) → Li 2 S (3)
Li (M) + S _z ⁿ⁻ → Li ₂ S (4)
Thus, finally, the coating containing silicon oxide (SiO _x ), silicon sulfide (SiS _y , where 0 <y <2), lithium oxide (Li ₂ O), and lithium sulfide (Li ₂ S) is the negative electrode. Formed on the surface of the active material. Here, the film formed on the surface of the negative electrode active material is a lithium ion conductive glass solid electrolyte. In the formulas (1) to (4), a-SiO _x represents amorphous silicon oxide, M represents a metal or metalloid that can be alloyed with lithium, for example, Al, Si, Ge, and 0 <b ≦ 4.4, z> 2.

  In the present invention, amorphous silicon oxide is previously formed on the surface of a negative electrode active material made of lithium or a lithium alloy, and after assembling the battery, a non-aqueous electrolyte containing a polysulfide anion is injected. Thus, lithium, amorphous silicon oxide, and polysulfide anion react on the surface of the negative electrode active material, and the surface of the lithium-containing negative electrode active material contains silicon oxide, silicon sulfide, lithium oxide, and lithium sulfide. The lithium ion conductive coating can be formed in situ. By this method, the process is simple, the influence of moisture is avoided, and a nonaqueous electrolyte secondary battery advantageous for the production process can be manufactured.

  Furthermore, the present invention assembles a battery using a negative electrode in which amorphous silicon oxide is formed on the surface of a negative electrode active material made of lithium or a lithium alloy and a positive electrode containing sulfur, and then injects a non-aqueous electrolyte. The battery is charged and discharged. In this case, the positive electrode active material may be sulfur, or the positive electrode active material may be a lithium composite oxide, and the positive electrode may contain sulfur.

In this case, soluble polysulfide (Li _{x Sn} ) was generated from sulfur in the positive electrode without dissolving the polysulfide in the electrolytic solution, and this was generated by partial dissociation in the electrolytic solution. It moves to the negative electrode together with polysulfur radicals (.S _n ²⁻ , where n> 4), polysulfur anions (S _n ²⁻ ), etc., and is charged and discharged to the surface of the negative electrode to form silicon oxide, silicon sulfide, lithium oxide and sulfide. A lithium ion conductive coating containing lithium is formed.

In the present invention, the “polysulfide anion” refers to partially dissociated Li _x S _n ^m− , polysulfur radical / S _n ²⁻ and polysulfur anion S _n ²⁻ .

  In this way, a nonaqueous electrolyte secondary battery using a negative electrode whose surface is protected with a lithium ion conductive film can be produced by an in situ electrochemical reaction at room temperature.

  Furthermore, the present invention, after assembling a battery using a negative electrode in which amorphous silicon oxide is formed on the surface of a metal or metalloid that forms an alloy with lithium and a positive electrode including a lithium composite oxide in a discharged state, A non-aqueous electrolyte secondary battery is manufactured by injecting a non-aqueous electrolyte containing a polysulfide anion and charging and discharging the battery.

  According to this manufacturing method, by charging the battery, lithium ions are generated from the lithium composite oxide in the discharged state of the positive electrode, and the surface of the metal or metalloid that forms an alloy with lithium forming amorphous silicon oxide Lithium is electrodeposited to form a lithium alloy. Subsequently, the polysulfide anion in the electrolyte moves to the surface of the lithium alloy, and the lithium alloy, amorphous silicon oxide, and polysulfide react with each other. A non-aqueous electrolyte secondary battery using a negative electrode in which a lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide is formed in situ on the surface of the lithium alloy and the surface is protected by the coating Can be manufactured.

  In the present invention, a battery is assembled using a negative electrode in which amorphous silicon oxide is formed on the surface of a metal or metalloid that forms an alloy with lithium, and a positive electrode containing sulfur and a lithium composite oxide in a discharged state. Thereafter, a non-aqueous electrolyte is injected to charge / discharge the battery.

According to this manufacturing method, lithium is first electrodeposited on the surface of a metal or metalloid that forms an alloy with lithium that has formed amorphous silicon oxide, and a lithium alloy is formed at the same time. Sulfide (Li _x S _n ) is generated, and this is partially dissociated in the electrolytic solution to generate polysulfur radical (· S _n ²⁻ , where n> 4), polysulfur anion (S _n ²⁻ ), etc. Lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide, and lithium sulfide on the surface of the lithium alloy when the lithium alloy, amorphous silicon oxide, and sulfur or polysulfide react with each other. Is formed in situ, and a non-aqueous electrolyte secondary battery using a negative electrode whose surface is protected with a film can be produced.

Next, an example of a method for coating amorphous silicon oxide (SiO _x ) on the surface of metal lithium, a lithium alloy, or a metal forming an alloy with lithium will be described. When coating by spray spray plating, it is desirable to use amorphous silicon oxide having a particle size of 1 μm or less.

When this amorphous silicon oxide fine powder is spray-plated on the surface of metallic lithium in a dry room, the thickness of the amorphous silicon oxide layer is preferably 2 μm or less, more preferably 1 μm or less. When the film thickness is increased, the protective effect is good, but the ionic conduction resistance is increased, which affects the output of the battery. The film thickness can be determined from the mass change of the lithium sheet before and after the amorphous silicon oxide coating and the powder density of the amorphous silicon oxide. This negative electrode is roll-pressed at a pressure of 20 kg / cm ² and used for a battery.

  When a Li—Si alloy is used as the lithium alloy, it is preferable to mix particulate Li—Si and the amorphous silicon oxide fine powder at a mass ratio of 95: 5 or more, and a mass ratio of about 99: 1. Is most preferred. When the amount of amorphous silicon oxide increases, the lithium ion conductive film of the final product increases as in the case of the lithium foil, leading to an increase in the internal resistance of the battery. Moreover, these mixtures are mixed with a planetary ball meal and used for production of an electrode plate.

  When using a vacuum evaporation method, an induction heating source, an electron beam thermal evaporation source, or the like is used. In this case, the film thickness of the amorphous silicon oxide can be controlled to 1 μm or less. Note that an RF sputtering method can be used. In the above case, since it is necessary to bring the electrolytic solution into contact with the underlying lithium in the subsequent manufacturing process, it is desirable to form a porous amorphous silicon oxide film.

  When a lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide is formed on the negative electrode surface, the lithium metal or lithium in the lithium alloy in a charged state is blocked from contact with the electrolyte. As a result, capacity loss due to side reaction of lithium in the battery is avoided in the charge / discharge cycle. Accordingly, it is possible to obtain a non-aqueous electrolyte secondary battery that has little capacity reduction even when the charge / discharge cycle is repeated, has a high energy density, and is excellent in charge / discharge cycle performance.

In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material is not particularly limited, and the composition formula Li _x MO ₂ or Li _y M ₂ O ₄ such as LiCoO ₂ , LiNiO ₂ , MnO ₂ , LiMn ₂ O ₄ is not necessary. (Wherein M is a transition metal, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), a composite oxide, an oxide having a tunnel-like hole, a metal chalcogenide having a layered structure, or the like can be used. _Also, V ₂ O _5, LiFePO ₄ or LiNi _x Mn _{2-x O 4} can be used. Furthermore, organic sulfur such as sulfur and disulfide can also be used.

  When a positive electrode active material other than sulfur was used, a positive electrode plate was produced as follows. Polyvinylidene fluoride (PVdF) as a binder was dissolved in N-methylpyrrolidone (NMP) to prepare a solution having a concentration of 2.5% by weight. To this solution, acetylene black was added so that the weight ratio of PVdF to acetylene black was 3: 2, to prepare a slurry.

To this slurry, a positive electrode active material such as LiCoO ₂ is added so that the weight ratio of the total of PVdF and acetylene black to the positive electrode active material is 10:90, and stirred to obtain a paste-like positive electrode mixture. Prepared. A predetermined amount of this positive electrode mixture was uniformly applied to a current collector made of an aluminum foil having a thickness of 20 μm, dried, pressed, and vacuum dried at 140 ° C. In this way, a belt-like positive electrode sheet provided with a positive electrode mixture layer containing a positive electrode active material was produced. A positive electrode lead made of an aluminum piece having a thickness of 100 μm was welded to one end of the positive electrode sheet.

  When sulfur is used as the positive electrode active material, a large amount of a conductive agent is required because sulfur itself is an insulator. And it is preferable that sulfur is uniformly disperse | distributed in a electrically conductive agent. In order to maintain the conductive network, it is desirable that the conductive agent is firmly bound on the current collector.

  As the conductive agent used for the positive electrode, carbon particles having a particle size of 200 nm or more and 20 μm or less, metal fine particles such as Ti, Al, Ag, Cu, and Ni, metal fibers, carbon fibers, and a mixture thereof can be used. Further, the active material and the conductive agent are firmly bound onto a positive electrode current collector such as an aluminum foil, a nickel foil, or a stainless steel foil by a fluororesin such as PVdF, PTFE, PVdF-HFP as a binder. It is preferable.

  When using a lithium alloy for the negative electrode active material, a Li—Al alloy having an average particle diameter of 60 μm and a Li—Si alloy having an average particle diameter of 60 μm were used. These alloy particles and amorphous silicon oxide were weighed in an Ar circulating glove box (moisture and oxygen <1 ppm) to a mass ratio of 99: 1, placed in a port, and closed with a screw. Subsequently, a planetary ball meal was added, mixed at a speed of 300 rpm for 7 minutes, and processed for a total time of 13 hours and 12 minutes for 1 minute.

  Further, these mixtures are put again in the glove box, and the mixture, acetylene black and PVdF are weighed so as to have a mass ratio of 85: 5: 10, mixed to form a paste, and this paste is placed on the nickel current collector. And dried in vacuum at 120 ° C. for 5 hours. In this way, an electrode plate before glass electrolyte formation was obtained.

When using metallic lithium as the negative electrode active material, a nickel foil or stainless steel foil having a thickness of 16 μm, which is difficult to alloy with lithium and hardly corroded by polysulfide anions, was used as a current collector. The thickness of the metallic lithium was 50 μm, and was bonded onto the current collector at a pressure of 50 kg / cm ² .

  In the nonaqueous electrolyte secondary battery of the present invention, the solvent of the electrolytic solution was changed depending on the type of the positive electrode active material. When an oxide is used for the positive electrode active material, for example, a mixed solvent of ethylene carbonate and methyl ethyl carbonate or a mixed solvent of ethylene carbonate and dimethyl carbonate can be used. These mixed solvents include propylene carbonate, butylene carbonate, vinylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, 2-methyl-γ-butyllactone, acetyl-γ-butyrolactone, γ-valerolactone, sulfolane, 1,2- Dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolane, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl Carbonate, dipropyl carbonate, methylpropyl carbonate, ethyl isopropyl carbonate, dibutyl carbonate, etc. may be used alone or in combination of two or more. .

  When sulfur is used as the positive electrode active material, it is desirable to use an ether solvent as the solvent for the non-aqueous electrolyte. The ether organic solvent can be solvated with lithium ions and separated from the polysulfur anion, while obtaining an electrolyte having high conductivity. In particular, these solvents have an advantage that they react with metallic lithium to form oligomer SEI or polymer SEI layer (SEI = Solid Electrolyte Interface) on the surface thereof and do not excessively react with metallic lithium.

  Here, usable solvents include tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), dimethoxyethane (DME), diglyme, triglyme, crown ether, dioxolane (DOL), tetrahydropyran (THP), and the like. Can be mentioned. Since these solvents have both a donor property and an acceptor property, solvation of lithium ions is promoted. Moreover, the mixed solvent of these solvents and the said ester solvent can be used.

The electrolyte salt as the solute of the non-aqueous electrolyte is, for example, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiCF ₃ CF ₂ CF ₂ regardless of the positive electrode active material. SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ or the like can be used alone or in admixture of two or more. Among them, it is preferable to use LiPF ₆ as the electrolyte salt.

  In the present invention, as the separator, those used in conventional non-aqueous electrolyte secondary batteries such as polyethylene and polypropylene microporous membranes, or polyolefin microporous membranes such as microporous membranes combining these can be used. it can.

As the polymer electrolyte, a polymer electrolyte obtained by mixing a polymer and a lithium salt can be used. The polymer is represented by the chemical formula (CH ₂ CHR ₁ X) _n (where R ₁ is a methyl group or an ethyl group, X is an element of S, O, or N), and has a molecular weight of 100,000 or more, 4, It is preferable to use one having a value of less than 000,000. As specific examples of the polymer, polyethylene oxide (PEO) or polypropylene oxide (PPO) may be used alone, in a mixed system or crosslinked, or a copolymer or derivative.

As the lithium salt mixed with the polymer, for example, LiBF ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ (LiBETI) or the like is used alone or in combination of two or more. be able to. These supporting electrolytes have high ionic conductivity, and are advantageous in improving the efficiency of lithium dissolution / deposition Coulomb.

  These polymer electrolytes may be used as a film, or may be coated on the surface of the positive electrode active material. When present on the surface of amorphous silicon oxide, an inorganic / organic composite electrolyte phase is formed, a flexible protective film is obtained, and it is effective for improving the mechanical strength of the negative electrode protective film.

  Hereinafter, preferred examples of the present invention will be shown, but the present invention is not limited thereto.

[Battery components]
In the batteries of Examples and Comparative Examples, the following positive electrode plate, negative electrode plate, and electrolytic solution were used.

[Positive electrode plate]
A positive electrode plate using lithium cobaltate (LiCoO ₂ ) as an active material was produced as follows. Polyvinylidene fluoride (PVdF) was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare a binder solution having a PVdF concentration of 2.5% by weight. Acetylene black was added to this binder solution to prepare a slurry. The weight ratio of PVdF to acetylene black in this slurry was 3: 2. LiCoO ₂ was added to this slurry and stirred to prepare a positive electrode mixture paste. In the positive electrode mixture paste, the weight ratio of LiCoO ₂ , PVdF, and acetylene black was 90: 6: 4.

A predetermined amount of the positive electrode mixture paste was uniformly applied to one side of a current collector made of an aluminum foil having a thickness of 20 μm, dried, pressed to a porosity of 28%, and further vacuum dried at 140 ° C. . In the obtained positive electrode plate, the supported amount of LiCoO ₂ was 24 mg / cm ² . In this way, a belt-like positive electrode sheet provided with a positive electrode mixture layer containing LiCoO ₂ was produced. This was cut into a 2.5 cm × 2.5 cm test piece, and a positive electrode lead made of an aluminum piece having a thickness of 100 μm was ultrasonically welded to one end of the positive electrode sheet. This was designated as a positive electrode plate P1. Since the positive electrode active material contained in the positive electrode plate P1 is LiCoO ₂ , the positive electrode plate P1 is in a discharged state.

A positive electrode using sulfur (S) as an active material was produced as follows. Sulfur (S) and graphite fine powder (specific surface area of 270 m ² / g) as a conductive agent are mixed at a weight ratio of 15: 7 and uniformly dispersed by ball meal, and sulfur (S) and graphite fine powder (GC) are mixed. A mixture (S-GC mixture) was obtained. Next, 10 g of PVdF was dissolved in 100 ml of NMP to prepare a binder solution. The S-GC mixture was added to the binder solution so that S: GC: PVdF = 60: 28: 12 (weight ratio) and stirred to obtain a positive electrode mixture paste. This positive electrode mixture paste was uniformly applied to one side of an aluminum foil, dried, pressed, and then dried at 80 ° C. for 6 hours. In the obtained positive electrode plate, the supported amount of sulfur was 4.8 mg / cm ² . In this way, a belt-like positive electrode sheet provided with a positive electrode mixture layer containing sulfur was produced. This was cut into a 2.5 cm × 2.5 cm test piece, and a positive electrode lead made of an aluminum piece having a thickness of 100 μm was ultrasonically welded to one end of the positive electrode sheet. This was designated as a positive electrode plate P2.

In the positive electrode plate P1, an electrode plate in which 3% by mass of sulfur was added to the mass of LiCoO ₂ in the positive electrode mixture was produced, and this was used as the positive electrode plate P3.

[Negative electrode plate]
A metallic lithium negative electrode was produced as follows. Metal lithium having a thickness of 50 μm was pressed with a linear pressure of 50 kg / cm ² using a manual roll press machine, and attached to one side of SUS316 as a current collector. This was cut into 2.5 cm × 2.5 cm, a nickel ribbon as a lead was welded to the ear of the SUS316 current collector, and Kapton tape was attached to the surface of SUS316 that did not contain lithium. This was weighed and the mass was m ₁ . This was designated as a negative electrode plate N1.

  A negative electrode containing a lithium-silicon alloy (hereinafter referred to as “Li-Si alloy”) as a negative electrode active material was produced as follows. A Li—Si alloy having an average particle size of 70 μm, acetylene black as a conductive agent, and PVdF as a binder were mixed at a weight ratio of 85: 5: 10, and NMP was added to obtain a negative electrode mixture paste. This negative electrode mixture paste was applied onto a nickel foil current collector and vacuum dried at 120 ° C. for 5 hours. This was designated as a negative electrode plate N2.

  A negative electrode plate using aluminum as a metal forming an alloy with lithium was produced as follows. Aluminum powder having an average particle diameter of 60 μm, acetylene black as a conductive agent, and PVdF as a binder were mixed at a weight ratio of 85: 5: 10, and NMP was added to obtain a negative electrode mixture paste. This negative electrode mixture paste was applied onto a nickel foil current collector and vacuum dried at 120 ° C. for 5 hours. This was designated as a negative electrode plate N3.

A negative electrode plate having amorphous silicon oxide formed on the lithium surface was prepared as follows. The surface of the negative electrode plate N1 is spray-plated with an amorphous silicon oxide fine powder having a particle size of about 0.8 μm in a dry room, and the amorphous silicon oxide adhering to the back surface is wiped off. The amount of silicon oxide was adjusted. Furthermore, after pressing at a pressure of 20 kg / cm ² , the electrode plate was weighed again to make the mass m ₂ . The amount of spray plating was adjusted so that the amount of amorphous silicon oxide supported on the lithium surface at this time was (m ₂ −m ₁ ) /6.25=0.5 mg / cm ² . The negative electrode plate thus obtained was designated as N11.

  An amorphous silicon oxide thin film was formed on the surface of the negative electrode plate N1 using an RF sputtering apparatus installed in the dry room. The target used was SiO, and the plasma source was Ar plasma. The output was 200 W, but the substrate was not heated because the melting point of metallic lithium was low. First, reverse sputtering was performed for 2 minutes under the same conditions to remove the impurity film on the surface of the lithium metal, and then the sputtering time was changed to control the film thickness of the amorphous silicon oxide thin film. An amorphous silicon oxide thin film having a thickness of 0.2 μm was designated as a negative electrode plate N111, a 0.5 μm thick negative electrode plate N112, a 1 μm negative electrode plate N113, and a 2 μm negative electrode plate N114.

  A negative electrode including an active material in which amorphous silicon oxide was formed on the surface of a lithium-silicon alloy (hereinafter referred to as “Li-Si alloy”) was produced as follows. An Li—Si alloy with an average particle size of 70 μm and amorphous SiO with an average particle size of 0.8 μm were weighed in an Ar circulating glove box (moisture and oxygen <1 ppm) at a weight ratio of 99: 1, put into a port, Closed with screws. Subsequently, the port was installed in a planetary ball meal, and the mixing of 7 minutes at a speed of 300 rpm for 1 minute was repeated for a total of 13 hours and 12 minutes. The obtained mixture was weighed again in the glove box, this mixture, acetylene black as a conductive agent and PVdF as a binder were mixed at a weight ratio of 85: 5: 10, NMP was added, and a negative electrode mixture A paste was used. This negative electrode mixture paste was applied onto a nickel foil current collector and vacuum dried at 120 ° C. for 5 hours. This was designated as a negative electrode plate N21.

  A negative electrode including an aluminum powder formed with amorphous silicon oxide on the surface was prepared as follows. Aluminum powder with an average particle size of 60 μm and amorphous SiO with an average particle size of 0.8 μm are weighed in an Ar circulating glove box (water and oxygen <1 ppm) at a weight ratio of 99: 1, put in a port, and screwed Closed. Subsequently, the port was installed in a planetary ball meal, and the mixing of 7 minutes at a speed of 300 rpm for 1 minute was repeated for a total of 13 hours and 12 minutes. The obtained mixture was weighed again in the glove box, this mixture, acetylene black as a conductive agent and PVdF as a binder were mixed at a weight ratio of 85: 5: 10, NMP was added, and a negative electrode mixture A paste was used. This negative electrode mixture paste was applied onto a nickel foil current collector and vacuum dried at 120 ° C. for 5 hours. This was designated as a negative electrode plate N3.

Next, an excess amount of lithium and sulfur is added to tetrahydrofuran (THF) from which water has been removed by 3A molecular sieve, and the mixture is refluxed for 12 hours to dissolve the polysulfide anion Li _x S _y ^n-. A red solution was made. And from this solution, unreacted lithium and sulfur were removed by filtration to prepare a solution X1.

  After immersing the negative electrode plates N11, N111 to N114 and N21 in this solution X1 for 5 hours, these negative electrode plates were washed three times with THF and air-dried to thereby form silicon oxide, silicon sulfide on the surface of the negative electrode active material. Then, a negative electrode plate on which a lithium ion conductive film containing lithium oxide and lithium sulfide was formed was produced. The negative electrode plate produced from the negative electrode plate N11 was produced from N12, the negative electrode plate produced from the negative electrode plate N111 was produced from N121, the negative electrode plate produced from the negative electrode plate N112 was produced from N122, the negative electrode plate produced from the negative electrode plate N113 was produced from N123, and the negative electrode plate N114. The negative electrode plate produced from N124 and the negative electrode plate N21 was designated as N22.

[Electrolyte]
A solution prepared by dissolving 0.5 mol / l LiN (SO ₂ C ₂ F ₅ ) ₂ (hereinafter abbreviated as “LiBETI”) in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 2: 1. This was prepared as electrolyte Y1.

  A solution in which 0.3 mol / l LiBETI was dissolved in a mixed solvent of EC and DEC in a volume ratio of 2: 1 was prepared, and this was used as an electrolytic solution Y2.

  A solution in which 0.5 mol / l LiBETI was dissolved in tetrahydrofuran (THF) was prepared, and this was used as an electrolyte Y3.

[Production of test battery]
First, one positive electrode plate and one negative electrode plate are passed through one polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer separator having a thickness of 25 μm and a size of 30 mm × 30 mm. The power generation elements were sequentially stacked. Next, this power generation element was housed in an aluminum resin laminate case in which an aluminum layer was sandwiched between polyolefin layers. Subsequently, a test battery was obtained by pouring the electrolyte under reduced pressure and sealing.

  A cross section of the test battery is shown in FIG. In FIG. 1, 1 is a positive electrode plate, 2 is a negative electrode plate, 3 is a separator, 4 is a positive electrode terminal, 5 is a negative electrode terminal, 6 is silicon oxide, silicon sulfide, lithium oxide and lithium sulfide formed on the surface of the negative electrode active material. It is a coating containing.

[Test conditions]
In the case of a battery using P1 for the positive electrode plate, the battery is allowed to stand for 10 hours or more after being manufactured, and then charged to 4.3 V at a constant current of 3.2 mA and discharged to 3.0 V at a constant current of 3.2 mA. The charging / discharging was repeated. The discharge capacity at the second cycle was defined as the initial discharge capacity. Since the discharge capacity decreases as the number of cycles increases, the number of cycles in which the discharge capacity is reduced to 50% of the initial capacity is defined as “cycle life”.

  In the case of a battery using P2 for the positive electrode plate, the battery is discharged to 0.5 V at a constant current of 0.5 mA, to 3.0 V at a constant current of 0.5 mA, and further to a constant voltage of 3.0 V for a total of 50 hours. Charging / discharging of charging was repeated. The discharge capacity at the first cycle was set as the initial capacity. In addition, in the open circuit state at the end of charging and at the end of discharging in each cycle, AC impedance measurement was performed at a frequency from 20 kHz to 10 mHz.

  In the case of a battery using P3 for the positive electrode plate, first, the battery was discharged to 1.8 V at a constant current of 3.2 mA at room temperature. Thereafter, charging / discharging of charging up to 4.3 V at a constant current of 3.2 mA and discharging up to 3.0 V at a constant current of 3.2 mA was repeated, and the discharge capacity at the second cycle was defined as the initial discharge capacity.

[Examples 1-3 and Comparative Examples 1-4]
[Example 1]
A battery A1 of Example 1 was produced using P1 as the positive electrode plate, N12 as the negative electrode plate, and 0.2 ml of Y1 as the electrolyte.

[Example 2]
A battery A2 of Example 2 was made in the same manner as Example 1 except that N121 was used as the negative electrode plate.

[Example 3]
A battery A3 of Example 3 was made in the same manner as Example 1 except that N22 was used as the negative electrode plate.

[Comparative Example 1]
A battery B1 of Comparative Example 1 was produced in the same manner as in Example 1 except that N1 was used as the negative electrode plate.

[Comparative Example 2]
A battery B2 of Comparative Example 2 was produced in the same manner as in Example 1 except that N11 was used as the negative electrode plate.

[Comparative Example 3]
A battery B3 of Comparative Example 3 was produced in the same manner as in Example 1 except that N2 was used as the negative electrode plate.

[Comparative Example 4]
A battery B4 of Comparative Example 4 was produced in the same manner as in Example 1 except that N21 was used as the negative electrode plate.

  The contents of the produced batteries of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1. In Table 1, “a-SiO” in the negative electrode surface coating represents amorphous silicon oxide.

  The test results for the batteries of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 2.

  Each battery after the charge / discharge cycle test was disassembled and subjected to XRD (CuKα) and XPS analysis of the negative electrode. As a result, it was found that a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide was formed on the negative electrode surface used in batteries A1 to A3 of Examples 1 to 3. However, in the battery B1 of the comparative example 1 and the battery B3 of the comparative example 3, there is no silicon oxide, silicon sulfide, and lithium sulfide on the negative electrode surface, and in the battery B2 of the comparative example 2 and the battery B4 of the comparative example 4, It was found that silicon sulfide and lithium sulfide were not present on the negative electrode surface.

  From the results of Tables 1 and 2, the following became clear. Although the initial discharge capacities of all the batteries were almost the same, a non-aqueous solution containing a layer of amorphous silicon oxide (a-SiO) on the surface of the lithium negative electrode or the lithium-silicon alloy negative electrode and containing a polysulfide anion was used. It was found that the cycle life of the batteries A1 to A3 of Examples 1 to 3 using the contacted negative electrode was superior to the batteries B1 to B4 of Comparative Examples 1 to 4. That is, in the negative electrodes used in the batteries A1 to A3 of Examples 1 to 3, the amorphous silicon oxide present on the negative electrode surface reacts with the polysulfide anion in the non-aqueous solution, and the surface is oxidized with silicon oxide and sulfide. By forming a lithium-ion conductive film containing silicon, lithium oxide and lithium sulfide, side reactions between the lithium negative electrode and the lithium-siliceous elemental alloy negative electrode and the electrolyte are suppressed, and further, the lithium-siliceous elemental alloy negative electrode In this case, it is considered that a function of relaxing expansion and contraction of the alloy phase is provided, and the cycle life is considered to be improved.

  On the other hand, in the batteries of Comparative Example 1 and Comparative Example 3, the amorphous silicon oxide was not originally present on the negative electrode surface, and in the batteries of Comparative Examples 2 and 4, the amorphous silicon oxide was not present on the negative electrode surface. However, since the negative electrode is not immersed in a non-aqueous solution containing a polysulfide anion, there is no sulfur source, and a film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide is not formed on the negative electrode surface. Due to side reaction between the negative electrode active material and the electrolytic solution, and when the negative electrode active material is a lithium-silica-based elementary alloy negative electrode, the cycle life is shortened due to poor current collection due to expansion and contraction of the alloy phase. It is thought to be a thing.

[Examples 4 to 6]
[Example 4]
A battery A4 of Example 4 was made in the same manner as Example 1 except that N122 was used as the negative electrode plate.

[Example 5]
A battery A5 of Example 5 was made in the same manner as Example 1 except that N123 was used as the negative electrode plate.

[Example 6]
A battery A6 of Example 6 was made in the same manner as Example 1 except that N124 was used as the negative electrode plate.

  Table 3 shows the contents and test results of the fabricated batteries of Examples 4 to 6. Table 3 also shows the results of the battery of Example 2.

  From the results of Table 3, the initial discharge capacities were almost the same in the batteries of Examples 2 and 4 to 6 using the negative electrode brought into contact with the non-aqueous solution containing polysulfide. It has been found that the cycle life improves as the thickness of the amorphous silicon oxide layer increases.

[Examples 7 to 9 and Comparative Examples 5 to 8]
[Example 7]
Example 1 except that N11 was used as the negative electrode plate, the negative electrode was not brought into contact with the non-aqueous solution containing the polysulfide anion, and a mixed solution of 0.05 ml of X1 and 0.2 ml of Y2 was used as the electrolytic solution. In the same manner as described above, a battery A7 of Example 7 was produced.

[Example 8]
A battery A8 of Example 8 was made in the same manner as Example 7 except that N111 was used as the negative electrode plate.

[Example 9]
A battery A9 of Example 9 was made in the same manner as Example 7 except that N21 was used as the negative electrode plate.

[Comparative Example 5]
Example 7 except that N1 was used as the negative electrode plate, the negative electrode was not brought into contact with the non-aqueous solution containing polysulfide, and a mixed solution of 0.05 ml of X1 and 0.2 ml of Y2 was used as the electrolyte. Similarly, a battery B5 of Comparative Example 5 was produced.

[Comparative Example 6]
A battery B6 of Comparative Example 6 was produced in the same manner as in Comparative Example 5, except that N2 was used as the negative electrode plate.

[Comparative Example 7]
A battery B7 of Comparative Example 7 was prepared in the same manner as in Example 1 except that N11 was used as the negative electrode plate, the negative electrode was not brought into contact with the nonaqueous solution containing polysulfide, and 0.2 ml of Y2 was used as the electrolyte. Produced.

[Comparative Example 8]
A battery B8 of Comparative Example 8 was produced in the same manner as in Comparative Example 7, except that N21 was used as the negative electrode plate.

  The contents of the batteries of Examples 7 to 9 and Comparative Examples 5 to 8 produced are shown in Table 4.

  The test results for the batteries of Examples 7 to 9 and Comparative Examples 5 to 8 are shown in Table 5.

  Each battery after the charge / discharge cycle test was disassembled and subjected to XRD (CuKα) and XPS analysis of the negative electrode. As a result, it was found that a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide was formed on the negative electrode surfaces used in the batteries A7 to A9 of Examples 7 to 9. However, in the battery B5 of the comparative example 5 and the battery B6 of the comparative example 6, there is no silicon oxide, silicon sulfide and lithium sulfide on the negative electrode surface, and in the battery B7 of the comparative example 7 and the battery B8 of the comparative example 8, It was found that silicon sulfide and lithium sulfide were not present on the negative electrode surface.

  From the results of Tables 4 and 5, the following became clear. The initial discharge capacities of all the batteries were almost the same, but after the batteries were assembled with a layer of amorphous silicon oxide (a-SiO) on the lithium negative electrode surface or lithium-silicon alloy negative electrode surface, polysulfide anions The batteries A7 to A9 of Examples 7 to 9 into which a non-aqueous electrolyte composed of a mixed solution of the non-aqueous solution X1 containing and the electrolyte Y2 was injected showed excellent cycle life.

  That is, in the negative electrodes used in the batteries A7 to A9 of Examples 7 to 9, the amorphous silicon oxide present on the surface of the negative electrode reacts with the polysulfide anion in the nonaqueous electrolytic solution, and the surface is oxidized with silicon oxide. The lithium ion conductive film containing silicon sulfide, lithium oxide and lithium sulfide is formed, so that side reactions between the lithium negative electrode and lithium-based elementary alloy negative electrode and the electrolyte are suppressed, and the cycle life is improved. it is conceivable that.

  On the other hand, in the battery B5 of Comparative Example 5 and the battery B6 of Comparative Example 6, since the amorphous silicon oxide originally does not exist on the negative electrode surface, even when the negative electrode is in contact with the polysulfide anion in the non-aqueous electrolyte, A lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide is not formed on the negative electrode surface. In addition, in the battery B7 of Comparative Example 7 and the battery B8 of Comparative Example 8, the negative electrode surface is amorphous. Although silicon oxide is present, since only Y2 is used as the non-aqueous electrolyte, there is no polysulfide anion in the non-aqueous electrolyte. Therefore, silicon oxide, silicon sulfide, lithium oxide and lithium sulfide are present on the negative electrode surface. Lithium ion conductive film containing is not formed. Therefore, in batteries B5 to B8 of Comparative Examples 5 to 8, the cycle life is shortened due to the side reaction between the negative electrode active material and the electrolytic solution.

  Further, in the comparison between Examples 1 and 7, Examples 2 and 8, and Examples 3 and 9, lithium ion conduction including silicon oxide, silicon sulfide, lithium oxide, and lithium sulfide on the negative electrode active material surface before assembling the battery. In comparison with the batteries of Examples 1 to 3 in which the conductive film was formed, the battery was assembled, and then the electrolyte solution was injected, and the surface of the negative electrode active material contained silicon oxide, silicon sulfide, lithium oxide and lithium sulfide on the spot. The batteries of Examples 7 to 9 on which the lithium ion conductive coating was formed showed excellent cycle life.

In the case of the batteries of Examples 1 to 3, the lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide formed on the surface of the negative electrode active material was dried before the battery was assembled. It is presumed that adverse effects such as reaction with trace moisture in the room, generation of harmful H ₂ S, and change in the composition of the coating will occur. Therefore, as a method of forming a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide on the surface of the negative electrode active material, the battery is more suitable than a method of forming a film on the negative electrode surface before assembling the battery. After assembly, a method of injecting an electrolytic solution containing polysulfide ions and forming a film in situ is preferable.

[Examples 10-12 and Comparative Examples 9-12]
[Example 10]
A battery A10 of Example 10 was made in the same manner as Example 7 except that P2 was used as the positive electrode plate.

[Example 11]
A battery A11 of Example 11 was made in the same manner as Example 8 except that P2 was used as the positive electrode plate.

[Example 12]
A battery A12 of Example 12 was made in the same manner as Example 9 except that P2 was used as the positive electrode plate.

[Comparative Example 9]
A battery B9 of Comparative Example 9 was produced in the same manner as in Comparative Example 5, except that P2 was used as the positive electrode plate.

[Comparative Example 10]
A battery B10 of Comparative Example 10 was produced in the same manner as in Comparative Example 6, except that P2 was used as the positive electrode plate.

[Comparative Example 11]
A battery B11 of Comparative Example 11 was produced in the same manner as in Comparative Example 7, except that P2 was used as the positive electrode plate.

[Comparative Example 12]
A battery B12 of Comparative Example 12 was produced in the same manner as in Comparative Example 8, except that P2 was used as the positive electrode plate.

  Table 6 shows the contents of the batteries of Examples 10-12 and Comparative Examples 9-12.

  Table 9 shows the test results of the batteries of Examples 10 to 12 and Comparative Examples 9 to 12.

  Each battery after the charge / discharge cycle test was disassembled and subjected to XRD (CuKα) and XPS analysis of the negative electrode. As a result, it was found that a lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide was formed on the negative electrode surface used in batteries A10 to A12 of Examples 10-12. However, in the battery B9 of the comparative example 9 and the battery B10 of the comparative example 10, there is no silicon oxide, silicon sulfide and lithium sulfide on the negative electrode surface, and in the battery B11 of the comparative example 11 and the battery B12 of the comparative example 12, It was found that silicon sulfide and lithium sulfide were not present on the negative electrode surface.

From the results of Tables 6 and 7, when sulfur is used as the positive electrode active material, the value of the initial discharge capacity is different, but regarding the cycle life, Examples 7 to 9 using LiCoO ₂ as the positive electrode active material and comparison It became clear that the same tendency as Examples 5-8 was shown.

[Examples 13 to 18 and Comparative Examples 13 and 14]
[Example 13]
After assembling the battery using P2 as the positive electrode plate and N11 as the negative electrode plate without bringing the negative electrode into contact with the non-aqueous solution containing polysulfide, 0.2 ml of Y3 was injected as an electrolyte, and the battery was kept for 10 hours or more. Then, charging and discharging were repeated three times at room temperature, discharging to 1.5 V at a constant current of 0.5 mA, and charging to 3.0 V at a constant current of 0.5 mA. did.

[Example 14]
A battery A14 of Example 14 was made in the same manner as Example 13 except that N111 was used as the negative electrode plate.

[Example 15]
A battery A15 of Example 15 was made in the same manner as Example 13 except that N21 was used as the negative electrode plate.

[Example 16]
A battery A16 of Example 16 was made in the same manner as Example 13 except that P3 was used as the positive electrode plate.

[Example 17]
A battery A17 of Example 17 was made in the same manner as Example 16 except that N111 was used as the negative electrode plate.

[Example 18]
A battery A18 of Example 18 was made in the same manner as Example 16 except that N21 was used as the negative electrode plate.

[Comparative Example 13]
A battery B13 of Comparative Example 13 was produced in the same manner as in Example 13, except that N1 was used as the negative electrode plate.

[Comparative Example 14]
A battery B14 of Comparative Example 14 was made in the same manner as Example 13 except that N2 was used as the negative electrode plate.

  Table 8 shows the contents of the batteries of Examples 13 to 18 and Comparative Examples 13 and 14 produced.

  The test results for Examples 13 to 18 and Comparative Examples 13 and 14 are shown in Table 9.

  Each battery after the charge / discharge cycle test was disassembled and subjected to XRD (CuKα) and XPS analysis of the negative electrode. As a result, it was found that a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide was formed on the negative electrode surfaces used in the batteries A13 to A18 of Examples 13 to 18. However, it was found that the battery B13 of Comparative Example 13 and the battery of Comparative Example 14 Battery B14 did not have silicon oxide on the negative electrode surface.

From the results of Table 8 and Table 9, the following became clear. The batteries of Examples 13 to 15 using P2 as the positive electrode and the batteries of Examples 16 to 18 using P3 as the positive electrode have different initial discharge capacities, but this is because the active material of the positive electrode P2 is sulfur. This is because the active material of the positive electrode P3 is mainly LiCoO ₂ and contains only a small amount of sulfur.

  In batteries A13 to A15 of Examples 13 to 15, the positive electrode active material was sulfur, an amorphous silicon oxide (a-SiO) layer was provided on the surface of the lithium negative electrode or the lithium-silicon alloy negative electrode, and the battery was assembled. Thereafter, the non-aqueous electrolyte Y3 was injected, the battery was allowed to stand, and then charged and discharged. By charging and discharging, sulfur of the positive electrode active material is dissolved in the electrolytic solution, and reacts with LiBETI in the electrolytic solution to produce a polysulfide anion, which reacts with amorphous silicon oxide on the negative electrode surface. In addition, by forming a lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide on the negative electrode surface, side reactions between the lithium negative electrode and the lithium-based elementary alloy negative electrode and the electrolyte are suppressed, The cycle life is considered to be improved.

  On the other hand, in the battery B13 of the comparative example 13 and the battery B14 of the comparative example 14, since the amorphous silicon oxide originally does not exist on the negative electrode surface, the positive electrode active material is sulfur, and after charging the electrolytic solution, charging and discharging As a result, sulfur as the positive electrode active material is dissolved in the electrolytic solution, and reacts with LiBETI in the electrolytic solution to produce a polysulfide anion. This polysulfide anion moves to the negative electrode surface, and the negative electrode is a nonaqueous electrolytic solution. Even when contacting with the polysulfide anion therein, a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide is not formed on the negative electrode surface. Therefore, in the battery B13 of the comparative example 13 and the battery B14 of the comparative example 14, the cycle life is shortened due to the side reaction between the negative electrode active material and the electrolytic solution.

  Here, as an example, the initial discharge characteristics of the battery A16 of Example 16 and the battery B13 of Comparative Example 13 are shown in FIG. In FIG. 2, the symbol ● represents the characteristics of the battery A16, and the ▪ represents the discharge characteristics of the battery B13. Moreover, the change of the alternating current impedance accompanying a charging / discharging cycle is shown in FIG. 3 in the case of battery A16, and in FIG. 4 in the case of battery B13. 3 and 4, the symbol ▲ indicates the initial charge state, ● indicates the first cycle full charge state, and ■ indicates the tenth cycle full charge state.

  Although there was almost no difference in the initial discharge capacity of FIG. 2, a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide was formed on the negative electrode surface shown in FIG. In the battery of Example 16, it is clear that the polarization is small and the impedance accompanying the charge / discharge cycle is stable as compared with the battery B13 shown in FIG. 4 in which the lithium ion conductive film is not formed on the negative electrode surface. It became. Thus, after the battery is assembled, the lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide formed in situ on the negative electrode surface in the battery is stable and improves cycle performance. It became clear that it was very effective.

[Example 19 and Comparative Examples 15 and 16]
[Example 19]
P1 was used as the positive electrode plate, N31 was used as the negative electrode plate, and the negative electrode and the non-aqueous solution containing the polysulfide anion were not brought into contact with each other, and a mixed solution of 0.05 ml of X1 and 0.2 ml of Y2 was injected as the electrolyte. After that, the battery is allowed to stand for 10 hours or longer, and then charged and discharged three times at room temperature to 3.2 V with a constant current of 3.2 mA and discharged to 3.0 V with a constant current of 3.2 mA. Was designated as Battery A19 of Example 19.

[Comparative Example 15]
A battery B15 of Comparative Example 15 was produced in the same manner as in Example 19 except that N3 was used as the negative electrode plate.

[Comparative Example 16]
A battery B16 of Comparative Example 16 was produced in the same manner as in Example 19, except that 0.2 ml of Y1 was used as the electrolytic solution.

[Comparative Example 17]
The contents of the produced batteries of Example 19 and Comparative Examples 15 and 16 are shown in Table 10.

  The test results for the batteries of Example 19 and Comparative Examples 15 and 16 are shown in Table 11.

  Each battery after the charge / discharge cycle test was disassembled and subjected to XRD (CuKα) and XPS analysis of the negative electrode. As a result, a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide was formed on the negative electrode surface used in battery A19 of Example 19, but this was used in Comparative Examples 15 and 16. It was found that no coating was formed on the negative electrode surface.

  From the results of Table 10 and Table 11, the following became clear. After assembling the battery using the negative electrode N31 having amorphous silicon oxide formed on the surface of aluminum, which is a metal that forms an alloy with lithium, and the positive electrode P1 containing a lithium composite oxide in a discharged state, a polysulfide anion Comparative Example Using Negative Electrode N3 That Was Supplied with Non-Aqueous Electrolyte Solution X1 + Y2 Containing and Charged and Discharged, but Battery A19 of Example 19 was Excellent, but Does Not Form Amorphous Silicon Oxide on Aluminum Surface In the case of the battery B15 of No. 15 and the battery B16 of Comparative Example 16 using the electrolyte Y1 not containing polysulfide anion, it was found that the cycle life characteristics were extremely short.

  In the battery A19 of Example 19, the lithium in the positive electrode moved to the negative electrode by the initial charge, and a lithium-aluminum alloy was formed in the negative electrode. The polysulfide anion in the electrolyte was amorphous silicon oxide on the aluminum surface. The lithium ion conductive coating containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide was formed on the negative electrode surface, thereby suppressing side reactions between the lithium negative electrode or lithium-based alloy negative electrode and the electrolyte. It is considered that the cycle life is improved.

[Example 20 and Comparative Examples 18 and 19]
[Example 20]
Using P3 as the positive electrode plate and N31 as the negative electrode plate, without bringing the negative electrode into contact with the non-aqueous solution containing polysulfide, after injecting 0.2 ml of Y1 as the electrolyte, the battery was allowed to stand for 10 hours or more. The battery A20 of Example 20 was repeatedly charged and discharged three times at room temperature with a constant current of 3.2 mA up to 4.3 V and a discharge of 3.0 mA with a constant current of 3.2 mA.

[Comparative Example 18]
A battery B18 of Comparative Example 18 was produced in the same manner as in Example 20 except that N3 was used as the negative electrode plate.

[Comparative Example 19]
A battery B19 of Comparative Example 19 was produced in the same manner as in Example 20, except that charging and discharging were not performed after leaving the battery.

  Table 12 shows the contents of the fabricated batteries of Example 20 and Comparative Examples 18 and 19.

  The test results for the batteries of Example 20 and Comparative Examples 18 and 19 are shown in Table 13.

  Each battery after the charge / discharge cycle test was disassembled and subjected to XRD (CuKα) and XPS analysis of the negative electrode. As a result, a lithium ion conductive film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide was formed on the surface of the negative electrode used in battery A20 of Example 20, but this was used in Comparative Examples 18 and 19. It was found that no coating was formed on the negative electrode surface.

  From the results of Table 12 and Table 13, the following became clear. After assembling the battery using a negative electrode N31 in which amorphous silicon oxide is formed on the surface of aluminum, which is a metal that forms an alloy with lithium, and a positive electrode P3 containing a lithium composite oxide and sulfur in a discharged state, The battery A20 of Example 20 charged with water electrolyte Y1 and charged / discharged had excellent cycle life characteristics, but the battery of Comparative Example 18 using the negative electrode N3 that did not form amorphous silicon oxide on the aluminum surface. In the case of B18 and the battery B19 of Comparative Example 19 in which charging / discharging after injection was not performed, it was found that the cycle life characteristics were extremely short.

  In the battery A20 of Example 20, lithium in the positive electrode moves to the negative electrode due to initial charging, and a lithium-aluminum alloy is formed in the negative electrode. At the same time, sulfur of the positive electrode active material is dissolved in the electrolytic solution. Reacts with LiBETI in the solution to produce a polysulfide anion, which reacts with amorphous silicon oxide on the aluminum surface, and lithium containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide on the negative electrode surface By forming the ion conductive film, it is considered that the side reaction between the lithium negative electrode or the lithium-based elementary alloy negative electrode and the electrolytic solution is suppressed, and the cycle life is improved.

The figure which shows the cross-section of the battery which becomes this invention. The figure which compared the first time discharge curve of the battery of Example 16 which becomes this invention, and the battery of the comparative example 13. FIG. The battery of Example 16 which becomes this invention, The figure which shows the alternating current impedance in the full charge state of each cycle. The figure which shows the alternating current impedance in the full charge state of each cycle of the battery of the comparative example 13 which becomes this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Positive electrode terminal 5 Negative electrode terminal 6 Film formed in the negative electrode active material surface

Claims (6)

In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing lithium or a lithium alloy, and a non-aqueous electrolyte, a film containing silicon oxide, silicon sulfide, lithium oxide and lithium sulfide is formed on the surface of the negative electrode active material. A non-aqueous electrolyte secondary battery characterized by comprising: 2. The nonaqueous electrolyte secondary according to claim 1, wherein the negative electrode active material comprising lithium or lithium alloy having amorphous silicon oxide formed on the surface thereof is contacted with a nonaqueous solution containing a polysulfide anion. Battery manufacturing method. A battery is assembled using a negative electrode in which amorphous silicon oxide is formed on the surface of a negative electrode active material made of lithium or a lithium alloy, and then a non-aqueous electrolyte containing a polysulfide anion is injected. The manufacturing method of the nonaqueous electrolyte secondary battery of Claim 1. A battery is assembled using a negative electrode with amorphous silicon oxide formed on the surface of a negative electrode active material made of lithium or a lithium alloy and a positive electrode containing sulfur, and then a nonaqueous electrolyte is injected to charge the battery. The method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein discharging is performed. After assembling a battery using a negative electrode formed with amorphous silicon oxide on the surface of a metal or metalloid that forms an alloy with lithium and a positive electrode containing a lithium composite oxide in a discharged state, the polysulfide anion is The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte solution is injected to charge and discharge the battery. After assembling the battery using a negative electrode in which amorphous silicon oxide is formed on the surface of a metal or metalloid that forms an alloy with lithium and a positive electrode containing sulfur and a lithium composite oxide in a discharged state, non-aqueous electrolysis is performed. The method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein the liquid is injected to charge and discharge the battery.

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